Researches on removal of the acetylene acting as a fatal toxic substance in a high molecular reaction of the ethylene have made a continuous progress up to now since 1950 year when the ethylene of high purity was required, and a typical process thereof has been a hydrogenation process using a catalyst.
It is disclosed in U.S. Pat. Nos. 2,511,453 and No. 2,735,897 that in early stage, chrome, cobalt, nickel, etc. and largely used with an intent to utilize cheap catalyst for the purpose of removing by a catalytic reaction the small quantity of acetylene contained in excessive ethylene. As a demand for ethylene of high purity was increased, however, it became necessary to develop a catalyst of higher selectivity. The critical line of small acetylene content in the ethylene has decreased continuously, that is, it was lower than 50-100 ppm in 1950s, but it became lower than 10-20 ppm in 1960s, and it is recently required to be lower than 5 ppm as a part of quality improvement of industrial products using the ethylene. Since the hydrogenation is effected in the presence of excessive ethylene, very high selectivity is required for it. In other word, it becomes in need of a catalyst to minimize loss of the excessively present ethylene caused by conversion of the ethylene into the ethane in the hydrogenation, and at the same time to hydrogenize selectively only the acetylene and convert it into the ethylene.
To this end, a palladium catalyst, a precious metal known as the most excellent one of transition metals in the aspects of activity and selectivity, even though it is high in price, was developed at the end of the 1950's (U.S. Pat. No. 2,927,141) and has been used practically in the industry since the middle of 1060s. The catalyst used now most widely is Pd/.alpha.--Al.sub.2 O.sub.3 which contains the palladium of 0.025-0.3 wt.% and the typical commercial catalysts are ICI-38-1 catalyst developed by the Imperial Chemical Industry Company, and Girdler G-583 developed by the Union Carbide Company.